Ball bearings comprise discrete rolling elements such as cones or balls captured in a circular race defined by inner and outer rings, and are used to reduce friction between relatively moving machine parts in contact with the inner and outer ring respectively. Cost of manufacture including material cost and assembly, and service life are paramount considerations in design of ball bearings. While such bearing can be machined from metals, the use of plastics is dictated in many applications, and this requires improvements in ways of fastening the bearing rings together for minimum friction in the races, long service life and minimum possible assembly time and effort for lowest cost in manufacturing.